I think there are two very distinct sides to Avery Brooks.
The side of Mr. Brooks that appears when he's on the job (acting, producing, teaching, etc.) is very professional and "normal." This is the side we see when he's playing the role of Sisko, when he's performing his duties as musical consultant in "The Captain's" documentary, and in a lot of the "official" interviews seen on the DVD sets.
Then there's the side of Mr. Brooks that we see in "The Captain's" documentary and at conventions. He's very much a free thinker and "eccentric" to a point where, IMO, it's uncomfortable to watch (breaking into song mid-sentence, making everything an issue related to racial injustice, etc.). I've heard this side be attributed to his being intoxicated, but I wouldn't put too much credit into it.